1. Field of the Invention
The invention relates to an assembly of optical element and mount, the use of such an assembly, an objective therewith and a projection exposure device for microlithography therewith. Optical components, such as lenses, prisms, mirrors, gratings, consisting usually of glass, crystal or ceramic, are regularly assembled by means of mounts, as a rule of metal, to give optical assemblies, for example, objectives.
The optical elements are then to be positioned while maintaining close tolerances relative to one another, and the whole assembly is to have a certain robustness against external influences. Particular requirements are then set both for astronomical telescopes, such as those in satellite-borne systems (for example, the ROSAT X-ray telescope), and in projection exposure systems for microlithography.
European Patent EP 0 053 463 teaches the suspension of precision mirrors on leaf spring elements, which are cemented.
A highly developed mounting technology for lenses of microlithographic projection objectives is also described in U.S. Pat. No. 5,428,482.
Either the lens is directly cemented with three radial bending beams, or an intermediate ring is connected to the outer mount ring by means of three monolithic joints evenly distributed on the periphery. Full-surface cementing of the lens and intermediate ring is provided. An optical assembly, in particular an objective, is then built up by stacking the mount rings.
Arrangements with actuators for the displacement or deformation of optical elements relative to the basic mount part are known in many embodiments. An example is provided by European Patent EP 0 145 902 A, where a mirror is suspended on a mount by means of three tangential spokes whose length can be varied by means of Peltier elements.